There are many uses for a vacuum source throughout society. Among the most common are uses in hospitals and paper mills.
In a typical installation, a large capacity vacuum tank will be maintained at a predetermined vacuum by a vacuum compressor. As the pressure rises in the tank during use, the vacuum compressor draws down the vacuum to the desired set point.
In many applications, the demand for the vacuum tank is non-continuous. For example, in a hospital the tank may see extensive use during the daylight hours, but be essentially unused through the night. Therefore, the compressor requires a control system which permits air to be pumped from the tank only when necessary. A typical control system uses a valve which closes off the connection between the tank and compressor to prevent air flow through the compressor. While the compressor may be operating on a continuous basis, because it is not compressing air when the valve is closed, very little energy is required.
When the system is first installed, and at periodic maintenance or service intervals, the tank will be at or near atmospheric pressure. When operations are to begin anew a severe strain is put on the vacuum compressor during this initial startup because the vacuum is essentially lost from the tank.
Traditionally, the industry has resolved the initial startup problem by putting a larger horse power motor, and perhaps an uprated vacuum compressor, to rapidly reduce pressure in the tank to the desired vacuum. However, during normal operations of the vacuum system, this excess horse power and capacity is usually unnecessary.